This project is concerned with elucidation of the biochemical behavior of the Ca2 ion/Mg2 ion ATPase present in human erythrocytes. One facet of the program is centered on the isolation of pure Ca2 ion/Mg2 ion ATPase using a calmodulin affinity column. Highly purified calmodulin, from human erythrocytes, has been prepared and is available in sufficient quantities to allow preparation of the affinity column. Detergent solubilized membranes will be used as the source of ATPase. Another part of the research effort will be directed towards identification of a substance thought to be a co-factor for the calmodulin activity. Finally the mechanism by which phospholipases A2 interact with membranes to cause loss of calmodulin stimulation will be explored. It is hoped that certain facets of the above program can be applied to an understanding of the alterations of the human erythrocyte upon aging.